1. Field of the Invention
The present invention relates to a method for heat-treating work in a predetermined atmosphere, and a heat treatment furnace used directly for carrying out this method.
2. Description of the Related Art
In heat treatment furnaces, typically such as continuous furnaces, used for processes such as carburizing steel parts, purge chambers, to which a purge gas such as an inert gas is supplied, are provided at the entrance and exit sides of a heat chamber, to which a predetermined process gas atmosphere such as CO or N2 is supplied, to isolate the inside of the heat chamber from the outside, thus improving the working environment and degree of safety, and moreover, stabilizing the atmosphere inside the heat chamber.
However, in a conventional heat treatment method and furnace such as the above, the inert gas inside the purge chamber has been known to break into the interior of the heat chamber when, for example, work is being transported from the entrance side purge chamber to the heat chamber, thereby disturbing the atmosphere inside the heat chamber so as to generate reduction of the concentration and partial pressure of the gaseous species of the atmosphere inside the heat chamber. As a result, problems have arisen in that work cannot be processed under the desired process conditions, leading to a deterioration of quality of the work being processed, or in that additional time is required to allow for the interior of the heat chamber to stabilize to the aforementioned process conditions, resulting in a deterioration in the process efficiency.
In consideration of the aforementioned problems with conventional art, an object of the present invention is to provide a heat treatment method and a heat treatment furnace employed in this method, which can prevent the occurrence of disturbance of the atmosphere inside a heat chamber, hence to prevent a deterioration of quality of the work being processed and process efficiency.
One aspect of the present invention is a heat treatment method for heating work inside a heat chamber supplied with a predetermined process gas atmosphere, while the interior of said heat chamber is isolated from outside air by means of a hermetically sealable purge chamber, wherein:
the inner pressure of said purge chamber is reduced to a predetermined pressure level;
said process gas atmosphere is supplied to the interior of thus evacuated purge chamber so as to backfill the inner pressure of this purge chamber substantially equal to the inner pressure of the heat chamber; and
said work is transported between the purge chamber and the heat chamber under the equalized pressure.
In the aforementioned heat treatment method, an atmosphere which is the same as that of the heat chamber is supplied to the interior of the purge chamber which has been pumped down to a predetermined pressure level, and by means of this atmosphere the inner pressure of the purge chamber is rendered substantially equal to that of the heat chamber, whereupon work is transported from one to the other. Thus, fluctuations of the concentration, pressure, and the like, of the atmosphere inside the heat chamber are suppressed to a great extent, and disturbance to the atmosphere can be prevented.
It is desirable in the aforementioned heat treatment method that the atmosphere is supplied gradually from the interior of the heat chamber to the interior of the evacuated purge chamber to render the inner pressure of the purge chamber and the inner pressure of the heat chamber substantially equal. In so doing, fluctuations of the pressure inside the heat chamber can be further reduced.
Another aspect of the present invention is a heat treatment furnace specifically suited to perform the method of the present invention as aforementioned.